The present invention relates to a piezoelectric actuator capable of efficiently moving a moving member, a method of driving a piezoelectric actuator and a computer readable storage medium stored with a program for making a computer execute a method of driving a piezoelectric actuator.
Currently, downsizing of OA apparatus and information processing apparatus has been progressed. In accordance therewith, attention is attracted to a piezoelectric actuator as a power supply used for driving and transferring. As an example of such a piezoelectric actuator, there is known an ultrasonic motor of a progressive wave type applying elongation and contraction operation on a piezoelectric element.
A progressive wave type ultrasonic motor is constituted by a stator and a rotor in a ring-like shape as shown by "Introduction to Ultrasonic Motor" by Kenjo, Shidacho, p.7, edited by Sogo Densi Shuppan. A piezoelectric oscillator comprising PZT ceramic is bonded onto a rear face of the stator by an adhering agent to thereby oscillate integrally therewith.
The piezoelectric member in the ring-like shape is divided into a plurality of small regions which are respectively polarized in directions alternately opposed to each other to produce a flexural wave of a progressive wave (refer to drawings at pp. 11 and 197 of the cited literature). Further, in order to apply sine wave voltages accompanied by phase differences on piezoelectric members at the respective divided regions, similarly divided metal electrode films must by formed. Further, in many case, the stator has a number of grooves or projections in a diameter direction in order to enlarge displacement. Such a complicated structure can easily be fabricated in the case of an ultrasonic motor having a diameter of several cm and therefore, there poses no problem. However, when a motor having a diameter equal to or smaller than 10 mm is desired, fine dimensional accuracy is required and the fabrication becomes considerably difficult with fabrication technologies currently used in the industry.
In order to resolve the above-described problem and realize a small-sized piezoelectric actuator having the diameter equal to or smaller than 10 mm, structures of an oscillator and a piezoelectric member may be constructed by a simple flat plate structure referred to as a unimorpl structure and there may be used a fabrication technology excellent in mass production performance of photolithography or etching.
However, as described on page 77 of the cited literature, according to the unimorph structure which is a simple structure of pasting together the oscillator and the piezoelectric member in the flat plate shape, there also poses a problem in which a flexural wave necessary for functioning the ultrasonic motor cannot be produced.
In order to resolve the above-described problem in the conventional technology, according to the invention, there is provided a method capable of producing a flexural wave even with the simple unimorph structure.
However, according to the above-described conventional micro piezoelectric motor 500 shown in FIG. 7, a flexural displacement mechanism unit 22 is oscillated at a primary mode and accordingly, there poses a problem in which produced torque is insufficient and a rotational number thereof is also small. Further description of the motor 500 is omitted here, reference being made to the detailed description of the motor 100 given hereinbelow.